On the morning of Friday 20th March was a major Solar Eclipse (peaking at ~85% obscuration at ~9:30am in Essex).
RSGB had a propagation experiment
and CARS Members were among those invited to participate.
RSGB had recommended that data be recorded over 08:15-11:30 GMT, and Murray G6JYB, acted as CARS coordinator.
An SDR-IQ Array was assembled at Danbury for LW/MW broadcast monitoring, whilst other CARS members had their own experiments on VLF and HF-WSPR.

VLF
Although it was totally cloudy in Chelmsford during the eclipse, a dip in the 23.4 kHz VLF signal
from the DHO38 transmitter in Germany was detected by Peter Meadows M0ZBU. This is shown in the plot below.
One characteristic of DHO38 is that the transmitter is switched off for an hour between 7 and 8 am.
Around the time of maximum eclipse there was a symmetrical dip in VLF signal strength.
The start and end times of the dip were 09:22 and 09:59 UT with the minimum strength being at 09:41 UT

VLF strength of DH038 on 23.4kHz received by Peter M0ZBU

The minimum strength time did not correspond to maximum eclipse here at the receiver (09:31 UT)
but to the maximum eclipse time at the transmitter site near Rhauderfehn, Germany at 09:41 UT.
The average of the start and end dips times is also 09:41 UT. Peter was not sure why this should be the case,
as he was expecting the minimum time to correspond to the mid-point between here and the transmitter.

Danbury SDR Array

At Clive G1EUCs qth in Danbury, an array of three RFSPACE SDR-IQs (CARS, Clive's and Murray's) was assembled and fed in equiphase from a single G5RV antenna.
Each SDR had its own PC running the Spectravue software so that 190kHz bandwidth spans could be recorded from three centre frequencies:-

SDR1: LW - 200kHz - for Radio Iceland

SDR2: MW1 - 800kHz - for BBC Scotland, Wales

SDR3: MW2 - 1300kHz - for others closer to the MUF

Almost all other equipment in the house was switched off in order to reduce the local noise floor.
At one point candle light was used rather than switching on LED lighting.
The collage opposite shows the three SDRs and their displays whilst the data was being captured continuously
and recorded as WAV files (10mins / 450MB each) over the three hours.

The data files enabled the entire event to be replayed through Spectravue for later analysis such as the BBC Scotland result below.

The best result for the eclipse (found so far) in the data was a very pronounced changed in the reception of BBC Radio Scotland on 810kHz
which came out of the noise and could be heard over the short period that totality was cooling the D-Layer. This tallied nicely with
similar results in Norwich. Of particular note is the twin-peaks which correlates with there being two co-frequency transmitters in Scotland at
Westerglen and Burghead.

BBC Radio Scotland on 810 kHz was a particularly marked increase as the D-Layer cooled

The Danbury event proved to be of interest to both amateurs and passers-by as we were having a
more intersting time on rf than those hoping to see the eclipse through overcast Essex clouds.

Murray G6JYB explaining the SDR1-LW waterfall to the Danbury Times delivery lady

Low-QRM Candlelight near totality

Many thanks to Clive G1EUC and Kristian 2E0SSX for their assistance/photos.

HF WSPR
Charlie M0PZT was running 1Watt of WSPR on 40m into a dipole 15ft agl and found that Swedish station SA0CAM popped up out of the noise on cue